Method of coating iron or steel articles with aluminum



. K. DELLGREN 2,135,388 METHOD OF COATING IRON OR STEEL ARTICLES WITHALUMI NUM Nov. 1 1938.

Original Filed Oc r,. 1, 1932 Zia/1 5 fleigmn/ I m ,4%

Patented Nov. 1, 1938 UNITED STATES PATENT OFFICE METHOD OF COATING IRONOR STEEL ARTICLES WITH ALUMINUM l lal 11 Claims.

The invention relates to a method of and apparatus for coating articlesof iron or, steel with aluminum in such a manner that the entire surfaceof the articles will be covered with aluminum and that on the surface analuminum-alloy is formed.

It is known for this purpose to dip the articles into a bath of moltensalts and subsequently into a bath of molten aluminum. It is furtherknown in the art of coating metallic articles with aluminum to provide areducing atmosphere over or on the top of the aluminum baths employed.

These known suggestions, however, failed to solve the problem in asatisfactory manner.

The articles to be coated with aluminum are subjected according to thepresent invention to a preliminary treatment preferably in a bath ofmolten salts and subsequently to a treatment in an aluminum bath whilethe same are kept within an atmosphere or zone of reducing gases free ofair or oxygen. In other words according to the present invention it isimperative that all air be removed from the furnace and a reducingatmosphere orzone be provided in the furnace preferably by introductionof suitable reducing gasesand the articles treated in the furnace areallowed to remain within said reducing atmosphere or zone for asuflicient length of time so as to be cooled therein. I

The bath of molten salts, preferably chlorides,

the aluminum bath and the atmosphere or zone on top thereof are kept atsuch a degree of temperature as will be suihcient to impart to thearticles the temperature required for the purpose in view.

As the iron or steel articles under treatment are exposed to the actionof an overlying atmosphere of purifying and reducing charactercontaining any of the known reducing agents such as chloride of zinc,chloride of ammonium and the like, which are known in the art to becapable of purifying metallic surfaces when in gaseous condition or ofreducing gases such as hydrogen, lighting-gas and the like, the outersurfaces of the same will be freed from oxide particles, so as to be inbest condition for the subsequent treatment in an aluminum bath.

The dipping-treatment in an aluminum bath is effected immediatelythereafter and without exposing the purified articles to the action ofair or any other injurious gases. The aluminum combines substantially atonce with the surfaces of the iron or steel or within a few seconds soas to form an alloy at the contacting surfaces of application October 1,1932, Serial No; Divided and this application March 1, 1937, Serial No.128,513

the article and a thin coating of aluminum is then deposited thereon.

The articles thus coated with an aluminum fllm are withdrawn from thefurnace through a channel or passage which'does not contain any air andis adapted to be cooled by water by means of a cooling jacket. In thisway the articles are cooled to such a degree that oxidation cannot setin, when the articles are subsequently passed into the outer air.

I shall now proceed to describe my invention more in detail with.reference to the accompanying drawing showing diagrammatically anapparatus or furnace especially constructed and adapted for carrying theinvention into effect.

Fig. 1 shows a vertical section of an apparatus suitable for carryingout my process. Fig. 2 is a vertical section of a modification thereof.

In the construction illustrated in Figure 1, A denotes the furnace and Bthe upper part of a chamber thereof filled with lighting-gas. Cindicates a crucible containing the molten salts and D denotes acrucible charged with aluminum in molten condition. The tube E in thetop of the furnace is provided with a valve and a covering cap andserves the purpose of introducing into the chamber B a substance, suchas ZnClz or NH4C] which will volatilize in the chamber due to the hightemperature prevailing therein so as to mix with the lighting-gas.

The iron or steel articles to be treated in the described furnace aresupplied to the crucible C by means of an air-tight closing winged wheelF. After the articles have been treated in the cmcibles C and D they aredischarged from the furnace through an inclined channel Q and through awinged wheel G similar to the wheel F, the housing of the wheel G istotally or partly enclosed in a cooling jacket K. The revolvingpaddle-boards L are provided for the purpose of forwarding the articlesthrough the two baths and into the channel Q as will be readilyunderstood upon inspection of Figure 1. M, M denote heating chambers forheating the crucibles C and D by means of suitable burners O, O. P, Pindicate outlet-channels for the hot combustion gases.

In some cases it will be advisable to employ a lead-bath or a bath ofany other suitable metal in lieu of the salt-bath C.

In the modification shown in Figure 2 separate juxtaposed crucibles aredispensed with. The modification of the furnace is especially intendedand adapted for use in coating iron or steel wire or band-ironin coiledform with aluminum, and is chiefly distinguished from the furshaped toform a vertical tube open at op osite ends and immersed with its bottomend in the bath C preferably of molten lead for preliminary treatment soas to fill or occupy the bottom end of the tube as will be readilyunderstood on inspection of Figure 2.

In the modification of the furnace shown in Figure 2 .obviously the bathfor preliminary treatment can be made or consist of metals or f alloysonly which are not susceptible of alligation with aluminum at all orsusceptible of such alligation to a very moderate degree only at thetemperature of about 700 C. required for coating iron or steel withaluminum. The furnace shown in Figure 2 is particularly adapted forcarrying out the present improved method in a continuous manner.

111 Figure 2 A indicates the furnace in general and C denotes a crucibleor container shaped and arranged to form a'cover at the top of thefurnace, so that the furnace-chamber M will be closed and notcommunicate with the outer air. The tubular opening S serves for theintroduction of the purifying or reducing gas into 'the room B enclosedby the cover R and the wire or band T to be coated with aluminum issupplied to the container or crucible C through a nozzle F' equippedwith suitable packing means. The wire or band is caused to pass throughthe metallic bath provided in the crucible C' and to run over a roller Uvertically upwards into the aluminum bath in the tube D and to bedischarged from the furnace through a stand-pipe or noz zle G which may.be integrally connected with the cover R. The said roller U is connectedwith the bottom end of the tube D.

M indicates the heating chamber or furnace properly speaking providedwith a burner 0' for heating the crucible C and with an outlet-channel Pfor the combustion gases to escape therethrough.

It is obvious that changes may be resorted to in the form andarrangement of the several parts without departing from the spirit andscope of my invention. Thus, for example, it may be advisable to protectthe bottom of the crucible D of the furnace shown in Figure 1 by meansof a layer of lead or any other suitable metal whichwill prevent themolten aluminum from exerting a dissolving action on the bottom of thecrucible.

case that the crucible is shaped to form a shallow container. a

This application is a division of my copending application Serial No.635,830; filed October 1, 1932.

I claim:

1. The method of coating iron and steel with aluminum which comprisespreliminarily heating the surface of the metal in the presence of anon-oxidizing gas under conditions that the same will be free from oxideparticles and will within a few seconds alloy with molten aluminum, andthen while still in a non-oxidizing atmosphere, introducing the heatedmetal into an aluminum bath having the surface thereof at the point ofentry of the metal in contact with the non-oxidizing gas. 2. The methodof coating iron and steel with This precaution is of Y. importance andespecially recommendable in aluminum which comprises preliminarilyheating the surface of the metal in the presence of a non-oxidizing gasunder conditions that the same will be free of oxide particles and willwithin a few seconds alloy with a coating layer of aluminum, and thenwhile still in a non-oxidizing atmosphere introducing the heated metalinto an aluminum bath, and removing the metin from said bath into anon-oxidizing atmosphere where it is subjected to conditions to cool thecoated metal.

3. The method of coating iron and steel with aluminum which comprisespreliminarily treating the base metal by heating the same in an.

ducting the same to'abath of molten aluminum.

4. The method described in claim 3 in which the base metal ispreliminarily raised to a temperature of 700 C.

' 5. The method of coating iron and steel with aluminum which comprisespreliminarily treating the base metal by heating the same in anatmosphere of a reducing gas under conditions to free the surface ofoxide particles and to permit the same to alloy within a few secondswith molten aluminum and then without exposing the base metal to anoxidizing atmosphere conduct ing the same to'a bath of molten aluminum,and thereafter positively cooling the aluminum coated metal in anon-oxidizing atmosphere before it is exposed to the air.

6. The process as described in claim 3 in which the base metal ispreliminarily raised to a temperature of 700 C. and wherein after thebase metal has been conducted through a bath of molten aluminum, thealuminum coated metal is positively cooled in a non-oxidizing atmospherebefore it is exposed to the air.

' '7. A method as described in claim 3 in which the base metal ispreliminarily subjected to a heated non-oxidizing bath.

8. The method as described in claim 3 wherein the base metal ispreliminarily subjected to a heated non-oxidizing'bath and is raised toa temperature of 700 C. before introduction 'into the bath of moltenaluminum.

9. The method as described in claim 3 wherein the base metal ispreliminarily subjected to a heated non-oxidizing bath and the aluminumcoated metal is positively cooled in a non-oxidizing atmosphere beforeit is exposed to the air.

10. A method as describedin claim 3 wherein' the base metal ispreliminarily subjected to a heated non-oxidizing bath and is raised toa temperature of 700 C. before introduction to the aluminum bath andwherein the aluminum coated metal is positively cooled ina'non-oxidizing atmosphere before it is exposed to the air. 11. Themethod of coating iron and steel with aluminum which comprisespreliminarily heating the surface of the metal in the presence of anon-oxidizing gas for a sufllcient length of time that the same will befree from oxide particles and will within a few seconds alloy withmolten KARL DELLGREN.

